Because conventional 2G/3G (second generation mobile communication/third generation mobile communication) networks include both CS (Circuit Switched, circuit switched) and PS (Packet Switched, packet switched) networks, the CS network may be used for a voice service, and the PS network may be used for a data service. However, for a 4G (fourth generation mobile communication) network, because a protocol of the 4G network defines the PS network only, a CS device is no longer available in the 4G network. However, the voice service is necessary in real life. Therefore, a 3GPP (the 3rd Generation Partnership Project) protocol specifies two voice solutions, which are CSFB (Circuit Switched Fallback, circuit switched fallback) and VoLTE (Voice Over Long Term Evolution, voice over long term evolution) separately.
The CSFB refers to that: when a user performs combined attachment to the 4G network, and needs to perform a voice telephone service, the user can notify a network side, then a network device actively enables the user to fall back to the 2G/3G network, and after falling back to the 2G/3G network, the user can perform a voice service by using the conventional CS network.
The VoLTE voice solution refers to that: a user directly makes a voice call in an LTE network by using an LTE bearer. However, in this solution, when the user moves from the 4G network to the 2/3G network, it is necessary to solve a problem of how to maintain voice call continuity by using an SRVCC (SingleRadioVoiceCallContinuity, single radio voice call continuity) technology.
The SRVCC technology refers to that: when a user moves to a coverage area of the 2G/3G network in a process of making a call in the 4G network by using the VoLTE, when an eNodeB (a base station) currently serving the user determines that both the current user and a network side support an SRVCC capability, and when a terminal reports that a destination side network is a GU (GSM EDGE Radio Access Network, UMTS Terrestrial Radio Access Network; Global System for Mobile Communications EDGE Radio Access Network, Universal Mobile Telecommunications System Terrestrial Radio Access Network) network, a base station may initiate an SRVCC process, and a handover from PS to CS is implemented with the cooperation between the network side and the terminal; and after moving to the 2/3G network, the user still uses a conventional CS device to make a voice call, and a voice service may not be interrupted.
In a current SRVCC scenario, a phenomenon of voice transmission interruption may occur.